A sealing material for semiconductors, LED and the like is required to have heat resistance capable of resisting heat generated by a working semiconductor device and LED. Furthermore, a sealing material for use in optical members such as LED is required to have transparency in addition to heat resistance. As these sealing materials, epoxy resin or silicone had been adopted. In the present specification, silicone refers to polymer compounds having a siloxane bond as a main backbone.
However, conventional sealing materials employing epoxy resin or silicone are not sufficient in heat resistance in the case of a sealing material for a power semiconductor or in the case of high-intensity luminous elements such as a high-intensity LED for automotive headlights or liquid crystal display TV backlights and semiconductor laser and the like, and had been known as bearing problems e.g. a leakage of current due to degradation of the sealing material, a problem of the sealing material becoming yellow etc. Hence a sealing material capable of resisting heat generated from a semiconductor formed containing silicon carbide (SiC) with high voltage resistance (such as a power semiconductor or a high-intensity luminous element) has been demanded.
Accordingly, it is possible to cite polyimide as a heat resistant resin for a sealing material.
For example, Patent Document 1 discloses a resin sealed semiconductor device characterized in that the device is provided with a semiconductor device having a ferroelectric film and a surface protective film and a sealing member formed of resin, the surface protective film being formed of polyimide, wherein the surface protective film is discussed as being cured by heating a polyimide precursor composition film at 230-300° C. However, a polyimide precursor composition is in a solid form around room temperature (20° C.), so that the composition is required to be in a condition dissolved in a solvent at the time of being applied to the device in order to seal the semiconductor device or luminous element. In other words it is not possible to conduct a potting process on the sealing material with no solvent. A potting process is a process of curing a resin liquid, a siloxane liquid and the like dropped on a surface of a substrate by heating them or irradiating them with ultraviolet rays so as to cause polycondensation or addition polymerization, or a process for sealing, for example.
As a material that allows the potting process without solvent and transparent and possibly serves as a heat resistant sealing material, silsesquioxane can be cited.
Silsesquioxane is a network polysiloxane obtained by hydrolysis and polycondensation of an alkyltrialkoxysilane or the like. Silsesquioxane allows such a molecular design as to take full advantage of the high heat resistance that the siloxane skeleton (an inorganic substance) has and the property of an organic group bonded thereto of, and therefore applicable to various uses. Moreover, some silsesquioxanes are in the form of liquid at room temperature, on which a potting process can be conducted.
A method for synthesizing silsesquioxane is disclosed in, for example, Patent Documents 2 to 7 and Non-Patent Documents 1 to 6. Particularly, a heat resistant sealing material that focuses on the transparency of silsesquioxane, for use in optical members such as LED and a semiconductor laser has variously been studied and disclosed in Patent Document 2 and Non-Patent Document 7, for example.
Additionally, in Patent Document 8, a silicon-containing curable composition that contains a platinum-based catalyst (a catalyst for curing reaction) is disclosed.
Furthermore, Non-Patent Document 8 discloses a method for synthesizing a siloxylithium compound and Non-Patent Document 9 discloses a method for synthesizing a disiloxane compound.